Study of the evolution of bacteriophages of Corynebacterium diphtheriae using DNA characterization procedures will be continued. An effort will be made to isolate a restriction fragment bearing the gene for diphtheriae toxin so that it can be used as a probe for the tox gene in phages and in strains of C. diphtheriae. The study of a set of new mutants (bin) will be extended to explore the hypothesis that heteroimmunity in the corynephages was a very early event in their evolution. The study of C. diphtheriae genetics has been extended to a search for plasmids and their possible role in gene transport among the corynebbacteria.